Chem 23 Finals

• Residue - the substance that remains in the filter paper
• Filtrate - the clear liquid or the substance collected after filtration
• Filtration - the method of separating insoluble impurities or substances from a liquid
• Size Exclusion Chromatography (SEC) also known as Gel filtration Chromatography is used for protein purification and separates molecules based on size.
• The gel consists of spherical beads made up of pores of specific size distribution.

  Molecules are separated based on their size and are eluted in order of decreasing molecular weight.
• Why SEC is so useful by separating proteins, based on size it can be utilized for

  • Desalting - this simply means we can remove salt and other small molecules from the sample.
  • Fractionation - since molecules of varying weights are separated within the gel matrix.
• Diffusion - movement of solute molecules from an area of higher concentration to an area of lower concentration  
• Osmosis - is the diffusion of solvent across a membrane, the movement of solvent molecules from a region of lower solute concentration to a region of higher solute concentration.
• Dialysis - is the process of separating molecules in solution by the difference in their rates of diffusion through a semipermeable membrane 
• Centrifugation

  • is the process of separation of insoluble materials from a liquid when normal filtration does not work well.
  • is based on the size, shape, density of the particles, viscosity of the medium, and the speed of rotation.
• The apparatus used for centrifugation is called a CENTRIFUGE.
• The centrifuge consists of a centrifuge tube holder called a ROTOR. The rotor holds balanced centrifugal tubes of equal amounts of the solid-liquid mixture.
• In Centrifugation, the denser particles are forced to the bottom and the lighter particles stay at the top.
• Extraction - utilizes differences in solubility

  Chromatography - utilizes differences in polarity.

  distillation - utilizes differences in boiling points
• The idea behind distillation is quite simple to understand. Given a mixture of two miscible liquids, if they have very disparate boiling points, we should be able to heat up the mixture to a temperature that is above the boiling point of one compound, but below the boiling of the other. This will cause the one with the lower boiling point to go into the gas phase, such that we can collect the vapor and condense it elsewhere, while the one with the higher boiling will just stay right where it is.
• A distilling flask, usually a round bottomed flask, is used to contain the mixture and boiling chips.
• The distilling flask sits above the heat source, which can be a hot plate, bunsen burner, or other heat source.
• The mixture is brought to a gentle boil, causing vapor to be produced.
• The vapor rises into the side arm, where a thermometer measures the temperature of vapor right as it approaches the horizontal section.
• The vapor continues into the condenser, which has a central hollow section where the vapor will pass, surrounded by another section where cold water will enter on one side and then exit from the other.
• The cold water in the condenser causes the temperature inside the condenser to drop, so when the vapor enters this section, it will condense back into a liquid.
• The liquid that condenses back into a liquid is called the distillate, and it is collected in a receiving flask.
• fractional distillation - this utilizes a fractionating column to separate mixtures with many components, like the atmosphere, or certain mixtures with industrial applications.
• azeotrope - this is a mixture of two or more liquids that when boiled, the vapor will contain those constituents in the same proportion as the liquid, and it will boil at a temperature lower than any of their individual boiling points.
• Sublimation is the property of a substance in which it is converted directly from solid to gas or vice-versa. Such substances are known as sublines. Some examples of solids that are subline are ammonium chloride camphor naphthalene and anthracene.
• After a sublime is heated it will directly get converted into vapor and this vapor will again condense at the upper colder part of the funnel to form a solid
• recrystallization - a solution for solid impurities.

  The way this works is that we will choose a very particular solvent in which to dissolve this solid. The solid must have a very low solubility in this solvent at room temperature, but a very high solubility in this solvent at very high temperatures, which makes sense given that solubilities will tend to increase as temperature increases, given the entropic favorability of dissolution.
•  precipitation reactions: when chemicals in a solution react to form a solid.

  A positively charged ion and a negatively charged ion held together by their charges might form a crystal when they're dry, but add a bit of water and those little polar molecules slide their way between the ions dissolving massive amounts of ionic compounds. But some ionic compounds can overcome even the dissolving power of water and when they form through reactions in solution, they fall out as a solid precipitate.
•  Cations are positively charged and anions are negatively charged. Just like little bar magnets, they attract. So cations only react with anions to form new compounds. And don't just think that there's one anion and one cation. The sodium ion in sodium chloride will have chloride ions on all four sides, which in turn are surrounded by four sodiums, and this pattern repeats many, many, many times until we end up with the salt crystals that we dissolved in the water.
• electroplating is a process in which metal atoms are transported onto the surface of another metal using electricity. As a result of this process the metal surface is plated in a thin layer of the imported atoms. electroplating is commonly used for decorative purposes and for preventing corrosion
• chromium is a metal which has high corrosion resistance and its appearance is aesthetically pleasing so chrome plating is used for decorative purposes providing corrosion resistance and increasing surface hardness besides chromium. zinc is also used for providing corrosion resistance the process of zinc electroplating is generally called galvanization.
• zinc is plated onto steel or iron to prevent rusting the zinc layer sacrifices itself and rusts over time so the plated metal is protected and this process is called sacrifice plating.
• Electroplating is carried out with a special device called an electrolytic cell.
• An electrolytic cell consists of a DC battery, electrodes, and an electrolytic solution.
• The electrode where atoms give electrons is called the anode.
• The electrode where atoms gain electrons is called the cathode.
• Oxidation reactions are carried out at the anode in electroplating.
• Reduction reactions are carried out at the cathode in electroplating.
• In electroplating, the anode should be positively charged and the cathode negatively charged.
• The metal to be used for plating must be connected to the anode in electroplating.